Production of fertilizers



Patented Dec; 21, 1943 UNITED STATES PATENT OFFICE raoncc'rroN ormarn'rzaas Property Custodian No Drawing. Application June 27, 1939,Serial No. 281,326. In Germany January 16, 1939 2Claims.

of monocalcium phosphatewith an appreciableproportion of calciumsulphate. .nIt is an object of the present invention 'to producefertilizers of a similar nature while avoiding the large ballast ofcalcium sulphate contained in the superphosphate" hitherto known. Afurther object of the invention is to increase the proportion ofphosphoric acid compounds which is converted into assimilable form,practically the whole of the phosphoric acid content of the finalproduct being present in the form of compounds which are both soluble incitric acid as well as ammonium citrate.

According to the present invention, raw pnosphates are mixed withphosphoric acid, preferably of at least about 40% concentration (HsPO4in H2O) in a quantity sumcient to convert the whole of the limecontained in the raw phosphate and which; is not already combinedthereinwithphosphoric acid (1. e., particularly as is present as calciumfluoride and/or calcium carbonate) into tricalcium phosphate, whereuponthe whole mixture is heated'to a temperature of at least about 1300" C.,and preferably to about 1350 C.

According to a modification of the invention such phosphates as arecapable of combining with the whole, or at least the greater part, oithe lime other than that already combined with phosphoric acid astricalciumphosphate, can be used instead of phosphoric acid. whenemployv ing an alkali metal phosphate for this purpose, the reactionwould proceed e. g. in accordance with the equations:

These equations are based on the employment of orthophosphates; howeverpyrophosphates or metaphosphates may be used instead. In this case ithas moreover'been observed that the althan alkali metal phosphates, afurther saving in phosphoric acid (both combined or uncombined) can beeffected by providing a further addition of alkali, e. g., in the formof soda ash, so-

I dium sulphate, potash, or potassium sulphate. In

this respect it has been found advantageous tov 1 provide about 0.5molof alkali oxide for every" mol of P205 contained in the rawphosphate.

When adding alkali to the reaction mixture and particularly when suchalkali is added in the form of alkali metal phosphate, it has beenobserved that decomposition of the raw phosphates already takes placewith lower heating temperatures, viz., at least about 1100" 0., andpreferably about 1250 to 1280 C. 7

Whilst when using phosphoric acid alone for the decomposition, a highsilica content of the raw phosphate is somewhat troublesome, this is notthe case when an addition of alkali is made to the reaction mixture; inthe latter case a relatively'high silica content of the raw phosphate isindeed desirable. The treatment with phos-' phoric acid alone is howeveralso applicable to raw phosphates rich in silica provided that lime isadded to the reaction mixture in such quantitles that the silica presentis converted thereby" into calcium silicates. Frequently however, it ismore advantageous to make up a burden in which raw phosphates rich insilica (e. g.,P ebble phosphate) are mixed with raw phosphates poor insilicaie. g., Morocco phosphates), since with a medium silica content(i. e., a content not exceeding about 4% S102 in the raw phosphates? thedecomposition with phosphoric acid alone leads to satisfactory results.

Moreover it is sometimes also advantageous to provide for a specialaddition of silica (sand) when treating-raw phosphates poor in silicawith phosphoric acid and alkali since, as has already been statemthepresence of silica promotes the decomposition in the presence of alkali.when the treatment is carried out with phosphoric acid alone, then thesilica content of the raw phosphate'must be at least about 3% in orderto arrive at a product of satisfactory solubility. If;; the silicacontent of the phosphate is less, then.

a corresponding amount oi silica must be added to the reaction mixture.

Examples 'an average diameter of 2-6'mms. are continuously supplied to arotary furnace in which a temperature of 1400 C. or 1280 0.,respectively, is maintained at'the end where the flame enters.

Total:P20s:"36.00%."'

according to whether phosphoric acid alone, or Jointly with alkali,isused for decomposition.

The small granules maintain their shapeduring. and porous and theheating process, are hard easily crushed.

1. To 25 kgs. of Pebble phosphate (32% P202,

47.8% CaO) are added 2.3 kgs. P205 in the form oi aqueous phosphoricacid (350 3. P205 per litre) and 1.5 has. of lime (CaO). The finalproduct 7 7 contains:

Total P205: 38.28%.

P202 soluble in citric acid:

36.38%=95% of the total P20: concentration.

P20: soluble in ammonium citrate solution:

28.54%=74.5% of the total P20; concentration. 7 F2 ;670.

2. To so me. Pebble "phosphate (32.0% P205,-

47,6% CEO) are added 7.50 kg8. of soda and 2.50

ka's. P205 in the form of aqueous phosphoric acid per litre). The finalproduct con P20: soluble in citricacid: I p

. 35.80%=99-.4% of the total P202 concentratlon. a

P202 soluble in ammonium citrate solution: I

I 34 .72%=06.5% of the total P202 concentration. p

32 To k'gs. oiPebble phosphate (32.0% P2012,

' 47.6% CaO) and 25 kgs. oi Morocco phosphate (34.2% P205, 40.64% 'CaO)are added 8.0 kgs. of soda .and 3.0 kksQPs Otinthe form of phosphoricacid. The final productcontains:

Total non- 37.41%. P202 soluble in citric acid: 7

35.98%.=96.2% of the total P205 tration. P205 soluble in ammoniumcitrate'solution: t

. a5.ao%=94.3% of themes P202 co es tration. 1 I": 0.09%. p V v 4; To 25m. or Pebble phosphate (32.0% P202. 47.022020) are added 2.94 kzs.NdsPaOmlOI-BO and 1.60kgs. of soda. The final product contains: 1 TotalP 05: 36.85%.

P20; soluble in citricv acid:

' '35.40 '=96.0% of the total P205 eenc nh -12 r P20: soluble inammonium citrate solution:

34.8 2%=94.4'% oi thetotal P202 concentration. 1

aqueous and about 1280' C.

5. To 25 kss. of Pebble phosphate (32% P20 47.6% 02.0) are added 2.4kss. Cal-1P0 and 2.2 kgs. Ca(H2PO4)2. The final product contains:

Total P205: 38.35%. P202 soluble in citric acid:

36.t38%=95% of the total P20: concentraon. P205 soluble in ammoniumcitrate solution:

' 28.54%=74.5% oi the total P205 concentration.

6. To 25 kgs. Morocco phosphate (34.2% P202, 47.6% CaO) are added 4.1kgs. soda, 1.25 kzs. P205 in the form of aqueous phosphoric acid and0.75 kg. Si02 (sand). The final productcontains:

Total P202: 37.79%. P205 soluble in citric acid:

' 37%39%=99% of the total P205 concentraion. p Z l V P205 soluble inammonium citrate solution:

36.21%=95.8% of the total'P2Ot concen- I tration. F: 0.15%. I V L Weclaim: r vNI 1. 'A process for the production of a fertilizer.

which comprises heating a mixture of raw phosphate, phosphoric acid, andan alkali metal compound of the group consisting of the alkali metalsulphates and carbonates and phosphates, the latter two ingredientsbeing present in such approximate amounts as are jointly just sufiicientto convert the lime contained inthe raw'phosphate not present thereinin. the form of tricalcium phosphate, into tricalciuin phosphate, andthe proportion of alkali metal compound being such that the mixturecontains about 0.5 mol of alkali for every mol of P205 contained in theraw phosphate, to a temperature of at least about 1100 C.

2. A process for the production of a fertilizer,

which comprises heating a mixture of raw phos-. 'phate, phosphoric acid,and an alkali metal compound of the groupconsisting oi the alkali metalsulphates and carbonates and phosphates, the

latter two ingredients being present in such ap-.

proximate amounts as are jointly just sufiicient to convert the limecontained in the raw phosphate not present therein in the form oftricalcium phosphate, intotricalciu-m phosphate, and the proportion ofalkali metal compound being such that the mixture'contains about 0.5 molof alkali for every znol of P205 contained in the raw phosphate, to atemperature between about 1250 rnmnnnn'r m.

manz RODIS. Kant. wm'rannonr'.

